Monoclonal antibodies (mAbs) have great potential as biodefense agents, whether in passive immunization, detection or disinfection. At present this potential is limited by the cost and time constraints in producing large quantities of these molecules. The most commonly used systems for monoclonal antibody production rely on transformed Chinese Hamster Ovary cells (CHO) grown in suspension culture. Production in CHO cells is a time-consuming process that is cumbersome and expensive to scale up to production volumes. In response to the need for a rapid and inexpensive system for the large scale production of mAbs, we have begun to develop eukaryotic algae as a production platform for the expression of human antibodies. We have successfully developed transformation vectors that allow for the expression of a variety of recombinant proteins, including scFvs, large single chain, and light and heavy chains of IgAs in the chloroplast of the unicellular green alga, Chlamydomonas reinhardtii. Under this proposal, we will expand upon these successes and demonstrate assembly of two classes of full-length human antibodies from both the chloroplast and nucleo-cytoplasmic compartments. Successful completion of this study should provide the proof of concept for using algae as a rapid means to produce large quantities of recombinant human antibodies. Specifically we propose to: 1) Optimize heterologous protein expression in alga chloroplast. 2) Assemble a Fab and full-length human antibody in algal chloroplast. 3) Express and assemble a Fab and full-length antibody from the nucleo-cytoplasmic compartment. 4) Carry out biochemical and cell based analysis of algal expressed antibodies in comparison with their mammalian expressed counterparts. 5) Scale up for production and purification of algal expressed antibodies.